Polyimides are condensation type polymers having a repeating unit of the type shown in Formula(A), below: ##STR4## where Ar is a suitable tetravalent organic (typically aromatic) radical, which may be a simple structure such as that derived from the benzene ring or a more complex structure such as that derived from benzophenone, or any other appropriate, usually aromatic, tetravalent radical; and Q is a divalent organic radical. The polyimide usually is made from the dianhydride of a suitable tetracarboxylic acid in one of two ways, as shown below. ##STR5##
Thus, dianhydride (B) may be first converted by reaction with diamine H.sub.2 NQNH.sub.2 into polyamide acid (C), which then can be chemically or thermally dehydrated to polyamide (A). Alternatively, dianhydride (B) may be first esterified with alcohol ROH, e.g., ethyl alcohol where R.dbd.C.sub.2 H.sub.5, to diester diacid (D), which forms with diamine H.sub.2 NQNH.sub.2 salt (E). This salt then is thermally cyclized to polyamide (A). Water and, in the appropriate case, alcohol is given off when (E) or (C) are subjected to high temperature and the polyamide results. In cases where copolymers are desired, as for this invention, the diamine compound includes a second diamine NH.sub.2 Q.sup.1 -NH.sub.2, which provides a unit similar to that shown as (C) or (F) except that a further polyamic acid or salt is also formed, i.e., ##STR6##
The prior art discloses that many of the totally aromatic polyimides are not easily processed since their crystalline melting points are well above the point where thermal decomposition occurs, i.e., about 450.degree. C. For example, typical infusible polyimides are formed with pyromellitic dianhydride and such varied diamines as m-phenylenediamine or 1,3-bis(4-aminophenoxy)benzene. These materials and related ones are difficult to fabricate on conventional processing equipment because of the high temperatures and pressures necessary to facilitate such operation.
It is known that in a somewhat similar class of polymers, the polyamide-imides, the melt ductibility and flow of the polymers are improved by blending in a polyether sulfone, i.e., polymers having the repeating units such as ##STR7## See for example U.S. Pat. No. 4,800,473.